fix(cashflow): net transfer categories in sankey (#257)

## Summary
- net transfer categories in the cashflow Sankey on their configured
side instead of showing gross signed flows
- keep the existing mixed-sign behavior for non-transfer categories so
regular income and expense categories can still appear on both sides
- add regression coverage for zero-net inflow transfers and partial
inflow/outflow transfer netting

## Testing
- vendor/bin/pint --dirty --format agent
- php artisan test --compact tests/Feature/CashflowAnalyticsTest.php
--filter=sankey

## Notes
- running the full `CashflowAnalyticsTest` file in this workspace still
hits two unrelated page tests because `public/build/manifest.json` is
missing locally

app/Http/Controllers/Api/CashflowAnalyticsController.php

@@ -181,30 +181,16 @@ class CashflowAnalyticsController extends Controller
     {
         $isIncome = $operator === '>';
 
-        // Group all transactions by category using the amount sign, not the category
-        // type. This allows one category to appear on both sides of the Sankey when
-        // it contains transactions of both signs (e.g. an income category that also
-        // holds property expense payments will show income on the left and the
-        // outgoing payments on the right).
-        $categorized = Transaction::query()
+        // Non-transfer categories keep the existing sign-based behavior so a
+        // category with mixed signs can appear on both sides of the Sankey.
+        $regularCategories = Transaction::query()
             ->where('transactions.user_id', $userId)
             ->whereBetween('transactions.transaction_date', [$from, $to])
             ->where('transactions.amount', $operator, 0)
             ->whereNotNull('transactions.category_id')
-            ->join('categories', function ($join) use ($isIncome) {
+            ->join('categories', function ($join) {
                 $join->on('transactions.category_id', '=', 'categories.id')
-                    ->where(function ($q) use ($isIncome) {
-                        $q->where('categories.type', '!=', CategoryType::Transfer)
-                            ->orWhere(function ($q) use ($isIncome) {
-                                $q->where('categories.type', CategoryType::Transfer)
-                                    ->where(
-                                        'categories.cashflow_direction',
-                                        $isIncome
-                                            ? CategoryCashflowDirection::Inflow
-                                            : CategoryCashflowDirection::Outflow,
-                                    );
-                            });
-                    });
+                    ->where('categories.type', '!=', CategoryType::Transfer);
             })
             ->select('transactions.category_id', DB::raw('sum(transactions.amount) as total_amount'))
             ->groupBy('transactions.category_id')
@@ -218,6 +204,37 @@ class CashflowAnalyticsController extends Controller
                 ];
             });
 
+        $transferCategories = Transaction::query()
+            ->where('transactions.user_id', $userId)
+            ->whereBetween('transactions.transaction_date', [$from, $to])
+            ->whereNotNull('transactions.category_id')
+            ->join('categories', function ($join) use ($isIncome) {
+                $join->on('transactions.category_id', '=', 'categories.id')
+                    ->where('categories.type', CategoryType::Transfer)
+                    ->where(
+                        'categories.cashflow_direction',
+                        $isIncome
+                            ? CategoryCashflowDirection::Inflow
+                            : CategoryCashflowDirection::Outflow,
+                    );
+            })
+            ->select('transactions.category_id', DB::raw('sum(transactions.amount) as total_amount'))
+            ->groupBy('transactions.category_id')
+            ->with('category')
+            ->get()
+            ->filter(function ($item) use ($isIncome) {
+                return $isIncome ? $item->total_amount > 0 : $item->total_amount < 0;
+            })
+            ->map(function ($item) {
+                return [
+                    'category_id' => $item->category_id,
+                    'category' => $item->category,
+                    'amount' => abs($item->total_amount),
+                ];
+            });
+
+        $categorized = $regularCategories->concat($transferCategories)->values();
+
         $uncategorized = Transaction::query()
             ->where('user_id', $userId)
             ->whereBetween('transaction_date', [$from, $to])

tests/Feature/CashflowAnalyticsTest.php

@@ -830,6 +830,129 @@ test('sankey includes inflow transfer categories on the income side', function (
     expect(collect($data['expense_categories'])->pluck('category.name'))->not->toContain('From Relatives');
 });
 
+test('sankey nets mixed-sign inflow transfer categories on the income side', function () {
+    $inflowCategory = Category::factory()->create([
+        'user_id' => $this->user->id,
+        'type' => CategoryType::Transfer,
+        'cashflow_direction' => CategoryCashflowDirection::Inflow,
+        'name' => 'From account of relatives',
+    ]);
+
+    $account = Account::factory()->create(['user_id' => $this->user->id]);
+
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $inflowCategory->id,
+        'amount' => 300000,
+        'transaction_date' => now(),
+    ]);
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $inflowCategory->id,
+        'amount' => -300000,
+        'transaction_date' => now(),
+    ]);
+
+    $response = $this->getJson('/api/cashflow/sankey?'.http_build_query([
+        'from' => now()->startOfMonth()->toDateString(),
+        'to' => now()->endOfMonth()->toDateString(),
+    ]));
+
+    $response->assertOk();
+    $data = $response->json();
+
+    expect($data['total_income'])->toBe(0);
+    expect($data['total_expense'])->toBe(0);
+    expect(collect($data['income_categories'])->pluck('category.name'))->not->toContain('From account of relatives');
+    expect(collect($data['expense_categories'])->pluck('category.name'))->not->toContain('From account of relatives');
+});
+
+test('sankey includes only the net positive amount for inflow transfer categories', function () {
+    $inflowCategory = Category::factory()->create([
+        'user_id' => $this->user->id,
+        'type' => CategoryType::Transfer,
+        'cashflow_direction' => CategoryCashflowDirection::Inflow,
+        'name' => 'From account of relatives',
+    ]);
+
+    $account = Account::factory()->create(['user_id' => $this->user->id]);
+
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $inflowCategory->id,
+        'amount' => 500000,
+        'transaction_date' => now(),
+    ]);
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $inflowCategory->id,
+        'amount' => -200000,
+        'transaction_date' => now(),
+    ]);
+
+    $response = $this->getJson('/api/cashflow/sankey?'.http_build_query([
+        'from' => now()->startOfMonth()->toDateString(),
+        'to' => now()->endOfMonth()->toDateString(),
+    ]));
+
+    $response->assertOk();
+    $data = $response->json();
+
+    expect($data['total_income'])->toBe(300000);
+    expect($data['total_expense'])->toBe(0);
+
+    $inflowIncome = collect($data['income_categories'])->firstWhere('category.name', 'From account of relatives');
+    expect($inflowIncome)->not->toBeNull();
+    expect($inflowIncome['amount'])->toBe(300000);
+    expect(collect($data['expense_categories'])->pluck('category.name'))->not->toContain('From account of relatives');
+});
+
+test('sankey includes only the net negative amount for outflow transfer categories', function () {
+    $outflowCategory = Category::factory()->create([
+        'user_id' => $this->user->id,
+        'type' => CategoryType::Transfer,
+        'cashflow_direction' => CategoryCashflowDirection::Outflow,
+        'name' => 'Investments',
+    ]);
+
+    $account = Account::factory()->create(['user_id' => $this->user->id]);
+
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $outflowCategory->id,
+        'amount' => -500000,
+        'transaction_date' => now(),
+    ]);
+    Transaction::factory()->create([
+        'user_id' => $this->user->id,
+        'account_id' => $account->id,
+        'category_id' => $outflowCategory->id,
+        'amount' => 200000,
+        'transaction_date' => now(),
+    ]);
+
+    $response = $this->getJson('/api/cashflow/sankey?'.http_build_query([
+        'from' => now()->startOfMonth()->toDateString(),
+        'to' => now()->endOfMonth()->toDateString(),
+    ]));
+
+    $response->assertOk();
+    $data = $response->json();
+
+    expect($data['total_income'])->toBe(0);
+    expect($data['total_expense'])->toBe(300000);
+
+    $outflowExpense = collect($data['expense_categories'])->firstWhere('category.name', 'Investments');
+    expect($outflowExpense)->not->toBeNull();
+    expect($outflowExpense['amount'])->toBe(300000);
+    expect(collect($data['income_categories'])->pluck('category.name'))->not->toContain('Investments');
+});
+
 test('breakdown includes unknown income category', function () {
     $incomeCategory = Category::factory()->create([
         'user_id' => $this->user->id,